niri: event-stream watcher to keep the agent workspace pinned at the bottom

[Kabilan108]

Deferred from the 2026-07-07 overnight niri-computer-use rebuild — revisit after living with the current setup for a few days.

Problem

The named "agent" workspace (background staging area for acu spawn --bg) is pushed to the bottom of the workspace list at session start (move-workspace-to-index 9 --reference agent in config.kdl). But niri's dynamic workspaces materialize from the trailing empty slot below it, so the agent workspace can drift up one position mid-session. Cosmetic only: Mod+0 targets it by name and stillsuit shows it as a mauve dot, so the index no longer matters for muscle memory.

Proposed fix (if the drift ends up annoying)

A ~40-line watcher (bin/agent-workspace-pin + systemd user unit, PartOf=graphical-session.target, Restart=on-failure):

1. Subscribe to niri msg -j event-stream; react only to WorkspacesChanged.
2. Invariant: agent workspace sits second-to-last on its output (right above niri's permanent trailing empty workspace).
3. On drift: niri msg action move-workspace-to-index 9 --reference agent. Converges in one step (the corrective move's own event passes the check); idempotent if races occur.
4. Intent heuristic so it never fights a human: keep the previous snapshot — re-pin only when the workspace count changed (drift case); if only the agent's index changed at constant count, that was a manual drag, leave it alone until next session.

Reliability notes: the event stream is the same feed stillsuit's bar consumes all day; niri dumps full state on every stream connect, so restart/reconnect can't miss drift.

Context

Built in Claude Code session 6522abba-e061-4616-8a64-131afea9f27c (transcript lands in ~/.local/share/tracer/archive/claude/dotfiles/6522abba-e061-4616-8a64-131afea9f27c.md once archived). Full environment findings: agents/skills/niri-computer-use/references/environment.md. Relevant commits: 994b0ee..596f508.

🤖 Generated with Claude Code

[Kabilan108]

Implemented in eb80863. The event-stream watcher now keeps the agent workspace above niri's trailing empty workspace while preserving constant-count manual moves.